1. Field of the Invention
The present invention relates to methods for decontaminating fluids, including protein-containing biological fluids, in particular blood products, other natural biologicals, and synthetic biotechnology products. The present invention also relates to apparatus useful for decontaminating fluids, including protein-containing biological fluids, in particular blood products, other natural biologicals, and synthetic biotechnology products. The present invention further relates to apparatus for contacting ozone with a liquid.
2. Discussion of the Background
Protein-containing biological fluids are important for a number of reasons. In particular, protein-containing fluids such as whole blood and blood products, such as red blood cells, platelets, and plasma, are important components of the health care system. Likewise, modern health care is also dependent on other important protein-containing biological fluids, including synthetic biotechnology products such as recombinant clotting factors, as well as natural biological products, such as antitoxins and vaccines. Unfortunately, the source of these fluids and the fact that these fluids contain proteins make them susceptible to contamination by a variety of infectious agents, such as parasites, bacteria, fungi, and viruses.
The common factor in all of these contaminants is that they contain DNA and/or RNA. Decontamination of the protein-containing fluid thus does not necessarily require the removal of the contaminating agents, but only the disruption of the contaminating agents' DNA and/or RNA so that these agents cannot propagate and thus spread disease.
The approach of attacking DNA and/or RNA is particularly useful in the blood industry because red blood cells, platelets and plasma, which are the useful components of blood for transfusion and pharmaceutical manufacture, contain no DNA or RNA. Furthermore, the leukocytes, or white blood cells, do contain DNA and RNA, but it is desirable to destroy this material to eliminate graft versus host disease (GVHD), as recently recommended for general transfusion practice.
Because of these potential benefits, several techniques have been developed to attack DNA and/or RNA in blood and blood products. The main target of this work is plasma, which is the straw-colored material left after the cellular blood components have been removed. Rich in proteins and nutrients, plasma can harbor many contaminants, but the smallest of the above contaminants, and thus the most difficult to treat, are the viruses. Specifically, potentially lethal viruses, such as HIV and Hepatitis B, are of great concern. These contaminants pose a great hazard when contaminated units are inadvertently included in the large pools of plasma used for the manufacture of pharmaceuticals, thus possibly leading to large scale infection among the treated population.
The existing techniques to eliminate such pathogens from plasma were recently summarized at the 1998 AABB annual meeting (Transfusion Transmitted Diseases (Prions; Bacteria and Parasites); Selected Topics in Transfusion-Transmitted Infections: American Association of Blood Banks Annual Meeting, The Compendium, 1998) and the 1999 CHI annual blood safety and screening symposium (Safety Issues: New Inactivation Technologies: Plasma; Cambridge Healthtech Institute's Fifth Annual Blood Safety & Screening Symposium, Feb. 23–24, 1999). These techniques can be roughly divided into two groups: (1) those that can treat only enveloped viruses, and (2) those that can treat both enveloped and non-enveloped viruses.
Beginning with the techniques that can treat only enveloped viruses, the most notable example is the solvent/detergent combinations that are specifically directed at the viral envelope itself. In particular, the Red Cross and V. I. Technologies are now actively promoting one such product as Plas+SD. Intended for direct transfusion, Plas+SD provides some degree of safety and uniform product consistency. There are, however, concerns over: (1) cost; (2) residual solvent/detergent left in the product; (3) the use of a donor pool, albeit a relatively small one at about 2,000 units; (4) the inability to treat non-enveloped viruses; (5) the impact of new or emerging viruses (A. Pereira; “Cost-effectiveness of transfusing virus-inactivated plasma instead of standard plasma,” Transfusion, vol. 39, pp. 479–487 (1999)); and (6) recent recalls (V. I. Tech Sees $3M, Or 24c/Shr 2Q Chg from Pdt Recall: Wall Street Journal/Dow Jones Newswires, Jul. 14, 1999).
Another technique for treating enveloped viruses is very high static pressure, on the order of 45,000 to 60,000 psi. However, the required pressure vessels are quite expensive and this technique, though used elsewhere (S. Denys et al, “Modeling conductive heat transfer and process uniformity during batch high-pressure processing of foods,” Biotechnol. Prog., vol. 16(1), pp. 92–101 (2000)), is still under development in the plasma industry. Beyond the limitation to enveloped viruses, there are also the practical problems of contamination and/or leaking of the pump oil, as well as rupture of the plasma bag. One variation is to freeze the plasma (D. W. Bradley, et al, “Pressure cycling technology: a novel approach to virus inactivation in plasma,” Transfusion, vol. 40(2), pp. 193–200 (2000)), but this process is relatively slow and raises the problem of freeze damage to the plasma proteins.
Of the many techniques capable of treating both enveloped and non-enveloped viruses, the most common example is intense light exposure. At high enough frequencies, in the UVC to gamma range, the energy in the light disrupts the basic structure of the contaminants. However, at these energies, there is also the problem of oxygen radical formation. To prevent these radicals from damaging the proteins, quenching agents are typically added to the plasma. Unfortunately, these agents are expensive, at least partially toxic, and must be removed before the plasma can be used. To avoid such problems, a limited exposure technique has recently been reported, but the results to date show only partial success, as well as some degree of protein damage (K. M. Remington, “Identification of Critical Parameters and Application to UVC Viral Inactivation in the Absence of Additives,” Cambridge Healthtech Institute's Sixth Annual Blood Product Safety Symposium, Feb. 13–15, 2000).
An extension of these direct light exposure techniques is the addition of a light-sensitive compound, such as methylene blue, to the plasma. When activated by light of the appropriate wavelength, this compound then attacks the contaminants. Like the above solvent/detergent processes, however, there are concerns over costs and the effects of residual material in the so-treated plasma.
Yet another approach commonly used for both enveloped and non-enveloped viruses is heat treatment, typically with steam. Obviously, however, this approach is not suitable for heat-sensitive proteins and is not used for single plasma units.
Finally, there are also other techniques under development, such as various ozone processes, but these processes are typically expensive and difficult to execute in the closed environment required for plasma processing. In addition, ozone-based methods suffer from the disadvantage of requiring long treatment times. On the other hand, ozone itself is cheap and is quite effective given sufficient processing time, and leaves no toxic residue (M. M. Kekez, S. A. Sattar; “A new ozone-based method for virus inactivation: preliminary study,” Phys. Med. Biol., vol. 42, pp. 2027–2039 (1997); U.S. Pat. No. 4,632,980; and U.S. Pat. No. 5,882,591).
To achieve better results, some of the above decontamination techniques have been combined. For example, the combination of the heat and solvent/detergent processes is quite effective against pathogens such as HIV (B. Horowitz; “Virus Inactivation by Solvent/Detergent Treatment and the Manufacture of SD-Plasma,” Vox Sang, vol. 74, Suppl. 1, pp. 203–206 (1998)).
Unfortunately, all of the above decontamination techniques, as well as others, have serious problems. The underlying difficulty is that the contaminant viral DNA and/or RNA are both proteins, any thus any technique that disrupts these contaminants can also cause significant damage to the desired proteins in the treated fluid. This is of great concern because damaged proteins are less effective clinically. For example, excessive decontamination damage of this protein will reduce the concentration in the fibrin glues used during surgery, and the resulting glue will thus not be capable of either approximating a wound or inducing hemostasis. Furthermore, damaged proteins also induce antibody formation, thereby making future treatment quite difficult (Barbara A. Konkle; “New Products for Patients with Hemophilia or von Willebrand Disease,” American Association of Blood Banks Annual Meeting, The Compendium, Baltimore, MD, pp. 111–115, 1998).
In addition, the contaminants and the desired proteins are also so similar that any technique that completely destroys all of the contaminants would also destroy all of the desired proteins. For this reason, no practical decontamination technology can be completely effective, and thus some small degree of contamination will always remain in the treated fluid. This is a particular problem for lethal contaminants such as HIV and Hepatitis B. In such cases, the goal is thus to reduce the contaminant as much as possible. In practice, acceptable levels are generally considered to be a logarithmic reduction factor (LRF) of 6, which means that 1 part in 1 million survives treatment.
Of course, because erythrocytes and platelets also have proteins similar to those found in contaminant, DNA and RNA, the problems of protein damage and incomplete decontamination also extend to these blood components.
Furthermore, similar problems also arise in the treatment of biologics other than blood products. Specifically, these other biologics, whether of synthetic or natural origin, should contain no untreated genetic material of their own, and should also not be contaminated with foreign DNA and/or RNA. On the other hand, the proteins in these biologics are similar to the proteins in the contaminating DNA and/or RNA. The net result of any treatment is thus again at least some protein damage, along with limited decontamination.
Finally, blood products and other biologics are also subject to several other problems. For example, in the modern health care environment, costs must be carefully controlled, both for capital equipment and any disposables. Likewise, technician time and training must be kept to minimum levels. Beyond these cost factors, however, there are also several process concerns. Specifically, the overall processing time must be kept as short as possible, as demonstrated by the recent and ongoing shortages in various intravenous immunoglobulins (IVIGs). In addition, there is only a limited supply of starting material, which must therefore be treated as efficiently as possible. Of course, all of the above concerns must be met, while also satisfying stringent regulatory requirements for safety and efficacy, along with full documentation.
The most difficult problem in decontamination work, however, is the possibility of contamination by agents that do not follow the normal DNA or RNA infection route. Specifically, recent work indicates that infections may also proceed by distortions in protein shape. In this case, the underlying agent is referred to as a “prion” and the resulting disease is commonly called “mad cow disease” in the bovine form, “scrapie” in the sheep form, and Creutzfeldt-Jakob Disease in the human form. Although their resistance to conventional decontamination technologies in fact characterizes prions, recent work indicates that these infectious agents may be at least partially susceptible to gamma irradiation, and possibly subject to sonic or ozone effects as well. It is therefore understood that the following techniques that are designed to protect proteins during decontamination for conventional agents can also be applied to protect proteins during prion decontamination.
A method for freeing blood and blood components of viable enveloped viruses by contacting the blood or blood product with ozone is disclosed in U.S. Pat. No. 4,632,980. U.S. Pat. No. 5,882,591 discloses a method and apparatus for disinfecting biological fluids, such as plasma/serum, through the interaction with gases, such as ozone.